When a vehicle fitted with tires with a semi-radial or radial carcass drives round a bend, modifications of the rolling conditions occur and, in particular, the footprint (i.e. the contact surface between the tread of each tire and the road on which the vehicle is rolling) can be very considerably modified in the shape of its contour and in its area. Bearing in mind the contact forces between the tire and said road, this leads to rolling behavior that can produce threshold phenomena which are difficult for a driver to control, especially at high speed.
In the configuration adopted when rounding a bend (cornering), the tires of a vehicle on the outside of the bend undergo transverse forces of greater or lesser intensity; these forces stem from the contact between the ground and the tread, and from the large vertical stresses that include the initial load supported by the tire and the overloads (some of the vehicle's tires are relieved of part of their load, to the detriment of the others). The outside of the bend means the side of the vehicle furthest away from the instantaneous center of rotation of said vehicle around the bend. In addition, the tire/wheel assemblies fitted on the outside of the bend are displaced transversely towards the outside of the bend relative to their footprint on the ground, and the outer sidewall of the tires is markedly stretched by the contact forces exerted by the road on the tread, which is pulled towards the inside of the bend (overall, the part of the tire tread in contact with the ground does not slide and follows a curved path corresponding to said bend). Under these conditions the geometry of the footprint changes and becomes essentially trapezoidal, the shorter side being towards the inside of the bend. The result of this is that the contact pressures on the part of the tread near the outer sidewall increase compared with the axially opposite part of the same tread. This new distribution of contact pressures perturbs the behavior of the tire during cornering.
For tires fitted to passenger cars it is felt necessary to provide technical solutions which enable the greatest possible reduction of the geometrical variation of the contact footprint of tires when cornering, and which limit as much as possible the variation of the contact pressure distribution under the same conditions.
The patent application published under number WO 02/09955 by the present applicants describes a new tire structure that can roll at high speed and can be subjected to more or less harsh drive or braking couples. To increase the resistance of the tire carcass reinforcement to these couples a solution is proposed in which the transverse and longitudinal rigidities of the sidewalls are increased, on the basis of a principle involving an additional reinforcement ring in at least one sidewall combined with the presence of a section of rubber mixture located between this additional ring an and anchoring element of the carcass reinforcement in each tire bead.
To improve both the tire's grip performance when cornering and to transmit the couples while ensuring better stability performance when cornering whatever the rolling speed situation, the tire according to the invention comprises two beads, a crown provided with a tread, and sidewalls connecting the crown to said beads. Each tire bead has an inclined portion located radially on the inside and designed to be in contact with a seat of a mounting rim, the seat being such that the points of said seat axially furthest on the outside are located on a circle of larger diameter than the points of said seat furthest on the inside. The mounting rim comprises flanges axially outside the seats to restrict the axial displacement of the beads during mounting on the rim.